The present invention relates to performance evaluation of a steam turbine steam path and, more particularly, to a steam path small particle impingement surface finish comparator for determining a numerical estimation of a steam path component surface roughness in micro-inches.
During the execution of a performance evaluation of a steam turbine steam path, the surface finish of both the diaphragm nozzles and the rotor bucket vanes is a significant factor for the determination of performance losses. Measurement of the surface finish is currently performed by using a portable electronic profilemeter and commercially available shot peen and grit blast comparator gauges. Neither of these methods, however, is applicable for surface roughness above 1000 micro-inches. The unique surface finishes produced in the turbine steam path by Small Particle Impingement (SPI) is typically in excess of 1000 micro-inches, and at present, there is no comparator available that replicates this SPI impact finish. The development of an SPI comparator for surface finishes in excess of 1000 micro-inches will serve to standardize the evaluation of SPI surface finishes within the turbine steam path.